A middlebox is a network appliance that manipulates Internet traffic by optimizing data flow across the network. Middleboxes can be configured as wide area network (“WAN”) optimizers and can be deployed in pairs across two geographically separated locations to optimize data traffic between the two middleboxes. Middleboxes can be connected through a single link or multiple links such as a leased line link and a broadband link. Middleboxes, which may be called WAN optimizers, can work as a pair of devices with a primary job of optimizing the network traffic and providing better user experience.
For high availability networks, it is common to establish secure connections between two end point entities, for example between a client device and a web server. One or more middleboxes can be deployed between the two end point entities. A middlebox can establish secure session connections with a client device, a server, or another middlebox, for example, using secure session layer (SSL) or a transport layer security (TLS) handshake protocol. Middleboxes can act either passively or actively. For example, a middlebox can passively act by just receiving any data from client device, server, or another appliance, and forwarding them to the next destination (e.g., client device, server, or another appliance). In this scenario, a middlebox does not play a significant role in contributing system optimization. When active, however, the middlebox can perform more than just receiving and forwarding of data. For example, the middlebox can modify communications received from client device, server, or another appliance and send the modified communication to the next destination (e.g., client device, server, or another appliance).